Question

# The mean lifetime of a tire is 37 months with a standard deviation of 8 months....

The mean lifetime of a tire is 37 months with a standard deviation of 8 months. If 127 tires are sampled, what is the probability that the mean of the sample would be less than 38.85 months? Round your answer to four decimal places.

Solution :

Given that ,

mean = = 37

standard deviation = = 8

n = 127  = 37  = / n = 8/ 127=0.71

P( <38.85 ) = P[( -  ) /  < (38.85-37) / 0.71]

= P(z <2.61 )

Using z table

=0.9955

probability= 0.9955

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